From CORNELL UNIVERSITY
ITHACA, N.Y. – When it comes to tackling climate change, the focus often falls on reducing the use of fossil fuels and developing sustainable energy sources. But a new Cornell University study shows that deforestation and subsequent use of lands for agriculture or pasture, especially in tropical regions, contribute more to climate change than previously thought.
The new paper, “Are the Impacts of Land Use on Warming Underestimated in Climate Policy?” published in Environmental Research Letters, also shows just how significantly that impact has been underestimated. Even if all fossil fuel emissions are eliminated, if current tropical deforestation rates hold steady through 2100, there will still be a 1.5 degree increase in global warming.
“A lot of the emphasis of climate policy is on converting to sustainable energy from fossil fuels,” said Natalie M. Mahowald, the paper’s lead author and faculty director of environment for the Atkinson Center for a Sustainable Future. “It’s an incredibly important step to take, but, ironically, particulates released from the burning of fossil fuels – which are severely detrimental to human health – have a cooling effect on the climate. Removing those particulates actually makes it harder to reach the lower temperatures laid out in the Paris agreement.”
She said that in addition to phasing out fossil fuels, scientific and policymaking communities must pay attention to changes in land use to stem global warming, as deforestation effects are “not negligible.”
While the carbon dioxide collected by trees and plants is released during the cutting and burning of deforestation, other greenhouse gases – specifically nitrous oxide and methane – are released after natural lands have been converted to agricultural and other human usage. The gases compound the effect of the carbon dioxide’s ability to trap the sun’s energy within the atmosphere, contributing to radiative forcing – energy absorbed by the Earth versus energy radiated off – and a warmer climate.
As a result, while only 20 percent of the rise in carbon dioxide caused by human activity originates from land use and land-cover change, that warming proportion from land use (compared with other human activities) increases to 40 percent once co-emissions like nitrous oxide and methane are factored in.
“In the short term, the land use tends to have twice the radiative forcing as it should have had from the carbon dioxide because of the co-emissions, so it’s twice as important,” said Mahowald.
Mahowald’s finding resonates with a previous paper she published in Global Biogeochemical Cycles in January, “Interactions Between Land Use Change and Carbon Cycle Feedbacks,” which showed that the carbon released by a deforested area is actually doubled over time because that area’s future potential to function as a natural sink – i.e., a habitat that can absorb carbon dioxide from the atmosphere – has been eliminated.
“Normally people only think about what’s happening right now when they think about the carbon budget,” Mahowald said. “But if you think about what’s going to happen over the lifetime of that land, long into the future, you should multiply that land conversion by two to understand the net effect of it.”
As agriculture expands in tropical areas and the pressures to turn forest into croplands increase, Mahowald stresses the importance of using extended timelines to assess the impact these practices have on the climate.
“We have a nice phrase: multi-centennial legacy of current land-use decisions,” she said. “When we think about climate change, we can’t stop at the end of the century. The consequences keep going for a couple more centuries.”
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I have never seen a study that determines if forty acres of soybeans sequester as much co2 as same acreage of forest.
Robert Long
It is not a trivial question, nor one easy to answer. Classic hardwood forests are near-deserts down under the trees, as the trees cut off sunlight to the forest floor and starve new growth out until forest fires and fallen large trees create a short-time open sunlight space. The large trees of course are very heavy with lots of leaf arrea. But they are few in number, with many meters between each large trunk. The many small trees previously trying to grow have all died out (been crowded out by the very successful tall trees that do survive), and so they have ALL “been converted back to CO2 by fires and by decay. (slow combustion as food for small plants and animales). But how many kilograms of moss remain after they “eat” a tree, and what are the long-term CO2 offsets for moss and fungi through a 150 year forest “lifetime”?
The open fields around dead trees (and the few power line cuts through a forest) are the ONLY places where new growth occurs, and thus the only places where CO2 is “stored” outaide of the few large (but heavy!) trees. A commercial field is growing tons of produce and vegetation every year. What is not harvested in plowed back under as mulsch and soil for the next year – again, better living through fungi and mold. The field is annually renewed, so is continually pulling CO2/recycling CO2 from the air into feed, food, fodder, fuel, and families.
The math – and, more importantly, the assumptions for the math – is not trivial.
That is my question in a nut shell
Cropland and grassland sinks 0.3 tons of Carbon per acre per year as long as it is not tilled. This has been carefully studied in many different places and that is the general value.
This is a higher number than forested land which is fairly low.
Zero-till crops and grassland worldwide sink about 1.0 billion tons of Carbon per year, forests are another 1.0 billion tons and oceans sink about 2.0 billion tons. This is compared to human emissions of about 9.5 billion tons.
Must have been a statement never to be made ?
Of course they focus on “greenhouse gases,” completely ignoring the major effects of deforestation. The effect of the loss of transpiration on rain patterns, the loss of the cooling effect of canopy shade, the changes in wind patterns…
See Biotic Pump Theory here: https://www.researchgate.net/publication/228528788_The_Biotic_Pump_Condensation_atmospheric_dynamics_and_climate
The authors of this article’s paper need to see that. The linked paper explains desertification, heat waves, increased land surface temperatures, all caused by deforestation – without once mentioning the evil bugaboo of greenhouse gases. GHG’s are largely irrelevant when the focus is properly placed on the benefits of natural forest to climate. Forestland doesn’t just hold the key to hydrological cycle stability, but also surface temperature stability Localized climate changes due to deforestation may have an effect on localized concentration of certain GHGs but the minor localized change in GHG concentration is effect, not cause.
This article is another example of misplaced focus on CO2 and “CO2 equivalent” forcings as the regulator of climate, another example of the perversion of science in the name of CAGW.
Even soybeans shade the dirt
I recall an article on early man in North America having s role in changing the climate in California by burning flora. Can’t seem to find it at the moment.
More recently, the Dust Bowl was caused by massive deforestation of the U.S.
No, it Was caused by a drought and poor plowing practices. Much of the dustbowl area had been without trees for many centuries prior to American settlement. It was open prairies.
Dr. Pielke, Sr., a very productive and ethical climate scientist, was ridiculed and shouted down for pointing out that land use changes are very important climate influences.
Simply because he dared to challenge the CO2 obsession if the consensus.
Now the weasels who have destroyed climate science as science, and turned it into a Lysenko style monster dare to to come back to land use.
In these papers[1][2], not one mention of increased photosynthesis as it directly links to earth’s energy budget[3], exists, only the effects on land use on CO2, whose effect on climate has not been sufficiently proven in the satellite era, is mentioned.
Photosynthesis is very efficient at transforming the visible spectrum of the TSI into something other than black body radiation, and is arguably the cause of Trenberth’s “missing heat”[4][5][6], even though the “missing heat,” itself, was not caused by CO2 in the first place[7].
Any warming produced by the increasing greenhouse gasses in the atmosphere would be evident in the lower troposphere as a reduction in the lapse rate, especially in the tropics where their has been no significant change beyond signal noise[8].
Removing those particulates actually makes it harder to reach the lower temperatures laid out in the Paris agreement.”……..
Back in around 1968 engineers showed that not only does cleaning the air result in an actual increase in temperatures by nearly a degree but it also results in an erroneous increase in the measured temperature of nearly as much because the Stevenson screen is not a perfect zero temperature rise effect enclosure. It rises in temperature considerably more in unfiltered sunlight of the now almost unbelievably cleaner air that in the pre industrial age let alone the Victorian industrial one.
The politicians and scientists have always had a contempt for engineers which they regard as vulgar trade and have in this case ignored their warnings of the incompetence and narrow training of climate scientists which means the scientist’s measurements are totally untrustworthy at the sub degree level. Perhaps we should have lied and over hyped the case as the climate fraternity have done and it is our fault for having the integrity not to do so.
Deforestation is obviously not in the official playbook of the advocacy cabal, mainly because it’s not centered in rich countries. The UN focus is on money farming and deforestation did not make the grade. It’s much easier to buy them off than to punish them and buying them off works if deforestation is not in the discussion. The same goes with pollution and ground water depletion.
The effect can be seen round Sao Paulo, where deforestation has created a dry micro-climate
Today there are more trees in the USA than there were 100 years ago.
It is possible that this is true of the whole planet also.
Received mantra is that trees are being lost by deforestation.
But CO2 enrichment of the atmosphere is increasing the number of trees.
Bond et al 2003 showed that in mixed tree-grassland ecosystems, past CO2 starvation caused a reduction in trees since tree saplings growing more slowly don’t grow big enough to survive the average interval between fires.
Thus less CO2 = less trees, and more CO2 = more trees.
http://onlinelibrary.wiley.com/doi/10.1046/j.1365-2486.2003.00577.x/full